Welding Propane Tanks

DenaliChuck said:

Have any of you welded fittings onto a propane tank?

I read that using forged (not cast) fittings is the best way; other advice?

What type of fitting would you use to weld on to connect two tanks together, and to provide input and output from the tanks?

How dangerous is it for a novice welder to attempt to weld onto a 15 psi tank?

This is a source of forged fittings that DaveBP provided http://www1.mscdirect.com/CGI/NNSRHM

Thanks!

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While there are many codes and regulations that differ, my take is that as long as you have the equipment and the skill to make a clean and bubble-free weld, there's no real risk in welding on a fitting for a low pressure tank that's to be filled with water as long as the temperature of the stored water is below boiling.. Even if the fitting failed suddenly, you'd only get the volume of your expansion tank venting through the hole. While that would be a mess, it wouldn't be an explosion. The total pressure on a welded fitting at 15 psi is only a couple hundred pounds at most - even I can make a weld that will hold that much.

I'd be much more apprehensive about a large weldment, such as an access hatch. If the tank is storing water at above boiling, it will flash to steam if pressure is reduced. That could be very dangerous.

Also run exhaust gas from a small generator / lawn mower , into tank before you start to weld or cut so you don't blow your self up . Old welder trick .
Anthony

The propane dealer I got my tanks from says the only (and probably faster) way to be absolutely certain all the propane is out of a tank is to fill it with water. I didn't want to put him on the spot and ask him what he does with the stinky water. Mercaptan is water soluble. Maybe somewhere far from the well.
System pressure is somewhere around 15PSI but the standard pressure relief valve is 30PSI. That's the number you want to add your safety factor to. That said, propane tanks are vastly overdesigned for residential boiler systems. My tank labels say 250PSI @ 350F. As long as you use forged,not cast or malleable fittings any weld that is leakproof will probably be plenty strong in the sizes that most of us are using. But I share Nofossil's hesitation about something like a manway or other large flange access for a heat exchanger. Larger weldments can develope weird strains and twists that add a lot of stress in addition to the working stresses. Welders that know their stuff can minimize that. It's not just a matter of piling up weld beads. I still use my old privy outhouse here in Maine yearround because I'm too cheap to pay for a septic system but I'm going to pay a certified welder to do my work.

When I was looking into welding on a used propane tank, I also came upon the exhaust trick, but was told that diesel was better than gas for that purpose.

i filled my tanks with water almost to the top. cut the holes i needed in them (with a torch) and welded in black iron fittings in while the tanks had water in them. then with the water still in the tanks plugged every hole and pressure tested them.

2.beans said:

i filled my tanks with water almost to the top. cut the holes i needed in them (with a torch) and welded in black iron fittings in while the tanks had water in them. then with the water still in the tanks plugged every hole and pressure tested them.

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That's definitely the best time to pressure test them. The air compressor would have to run a long, long time without the water taking up all that space.

Ron

But put in at least 1 1/4 couplings. You can always plug or bush them down.

locust loco said:

2.beans said:

i filled my tanks with water almost to the top. cut the holes i needed in them (with a torch) and welded in black iron fittings in while the tanks had water in them. then with the water still in the tanks plugged every hole and pressure tested them.

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That's definitely the best time to pressure test them. The air compressor would have to run a long, long time without the water taking up all that space.

Ron

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Not to mention - failure with compressed air could well be fatal. Pressure testing should always be done with water.

DenaliChuck said:

chuck172 said:

But put in at least 1 1/4 couplings. You can always plug or bush them down.

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Would 1 1/4 fittings be enough diameter to prevent flow from mixing the stratification in the tanks (especially the lines that connect the tanks)?

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I'd like to see if anyone out there has better ideas about tank fittings and stratification. My thoughts are that ideally you'd want a horizontal pipe along the top and bottom, each capped, and with bazillions of little holes so that water is introduced and withdrawn right at the very top and bottom at very low velocities. Perhaps such a contraption could be worked into place and welded in?

I think traditional DHW tanks use a large horizontal baffle to divert the flow to horizontal and reduce the velocity by the time it meets the standing water in the tank. Don't see how to do that in this case.

Perhaps the simplest approach would be to take a section of 2" pipe, weld a plate on the end, and drill a bunch of holes in the pipe near the end. Cut an appropriate diameter hole in the tank, insert this pipe to the desired depth (just a few inches for the top, all the way down for the dip tube) and weld it in place.

Any more ideas?

the first tanks a built i put the hot supply straight in the top and pull the cold return off the bottom with dip tubes. i get 15 degree temp change between the top of the tank and half way down the tank. i also get another 15 degree temp change from half way down to the bottom. this happens when im charging the tanks. as the tanks sit for a couple of days the middle and top get to be about the same temp with the bottom being at least 15 to 20 degrees cooler. this is with the tanks horizontal not stacked. i am in the process of building a tank as im typing with the supply going in the side top pointing horizotally. im thinking this might help stratify more. as for the ghost circulation i have a 3 way zone valve that isolates the tanks from the wood boiler when they hit my set temp and added a one way zone valve on the tank supply line after the three way zone valve to stop the water from ghost circulating. on the house side of the tank a use a taco IFC pump to stop ghost circulation.

I’ll weld a round plate on the end of a 30” section of 2” forged black pipe, thread the other end, and then drill a bunch of 1/8” holes down one side of the pipe. Repeat 3 more times.

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I'm planning to do the same thing. 2" capped pipe, bunch of holes.I like the up and down orientation, too. My intuition (not to be confused with understanding) is that the sum of the cross section areas of the holes should be at least the area of the 2" pipe. Especially since smaller holes have a lot more flow friction for the area they provide, probably need more total area for the holes. 1/8" dia. would need about 250 holes to provide the same area as the supply pipe; 1/4 about 64; 5/16 about 42; and 3/8 almost 30. I'm trying to design for minimum back pressure through the tanks so I'm thinking about larger holes. Back pressure is going to result in an increase in "nozzle" velocity coming through those little holes, too. Maybe counterproductive if too small.
Don't you just love these dilemmnas?

I am going the “vertical tanks/in series” route also. Since I’m putting a DHW coil in the top of the first tank I had my welder insert a horizontal section of 1 ¼” pipe about ¾ of the way down the curved end of the tank for the inlet/outlet. This placement serves two purposes. First, I wanted the inlet/outlet to be outside the circumference of the DHW coil. Second, I hope to decrease the “mixing effect” by causing the water to rotate around the tank as it enters. Try picturing what you see while stirring a glass of chocolate milk. The water won’t be entering or exiting fast enough to create the vortex that you would see in a glass. Therefore I don’t think that it will suck the hot water down the center like you would see in a water glass. Maybe I should have, but I did not do the same with the bottom of the first tank or the other two tanks. The other five inlets/outlets are all in the center of the tank ends.

Ron

Hi all
I have welded on tanks and boilers. I think it's better to weld the pipe into the tank and not the fitting. When you weld the fitting into the tank, welding (heat ) will make the fitting a little larger in diameter. Not a good thing. If you are going to weld in a fitting make sure that the fitting is for high pressure steam. The fitting is alot thicker. I always try to weld three passes of weld around any fitting. Pressure test and use dish soap, it will show if you have a leak.

Having a welder weld in the fitting is money well spent. If you want to weld, weld on your lawn mower.

On your down tube in the tank, 1/8" holes sounds to small. What happens when the holes rust? ( and they will )
Marcus

First let me say there are many good ideas contained on the Boiler Room. That being said, there has and bave been many questions as well as replies concerning welding, testing etc of pressure tanks. Unless you are an engineer or a welder who have experience with pressure vessels, THIS IS NOT A DIY PROJECT. After all codes and standards do not exist because this type of work is easy!

Even pressures that exist in home heating systems can cause injury or death with something that goes wrong. There is a lot of energy at the pressures and temperature's seen in these systems. Hot water heater explosions while rare are not unheard of. One of the reasons that heat storage systems such as that used for years by Tarm are not pressurized is that other then hot water scalding (bad enough) there is no overpressure.

If you want a pressurized system that will be from scratch, i.e. not purchased from reputable firm, see an engineer who knows about ASME codes or a reputable heating engineer.

i do believe that some people shouldn't even weld on there lawn mower let alone mow with it , but by the time you sit back and pay the so called professionals to build it for you it will be cheaper to burn wads of money to heat your house. there is alot of good info here and lots positive feedback. most people realize when a project is over there head. i believe this is a DIY project.

Denalichuck

Schedule 40 is what I would use.
Welders don't weld on a pressure vessel thinking it's only got to hold 30 pounds. You weld it to hold what ever the pressure.
If your pressure relief fails ( and they do ) is your weld going to hold?????????
I would keep asking around, maybe there is a welder closer than you think.

Marcus

marcuswayne has hit the nail, or nails on the head.

The pressure is low until something that "won't happen" does just that. I know Murphy's Law hasn't been repealed in my area yet ;-) If you end up doing the welding yourself, cap off your connections and test the tank in pressure steps until you are above a safety margin higher than your expected use range.

If you have the welding skill then best of luck to you. And if you are unsure of said skill level, then I echo the advise to continue looking for a welder. If actual businesses offering welding services are scarce, which sounds like your case, then try businesses that would use or employ them for their own use. Then hire them on the side.

Getting a leak is nothing, its the explosion that you should be worried about. When your welding on a propane tank, your welding on a bomb. Be careful!

Good move!